1. Field of the Invention
This invention relates to the translation of messages and responses being transferred between two different types of telecommunication networks. The messages are translated from the protocol of one network to the protocol of the other. More particularly, the invention relates to moving messages between a circuit-switched and a packet-based network. The invention is particularly useful to bridge the gap between an advanced intelligent network (AIN) and an internet protocol (IP) network that operates according to the session initiation protocol (SIP).
2. Description of the Problem
Evolution of the public switched telephone network (PSTN) has accelerated in recent years. Much of the PSTN still operates on circuit-switched connections. Integrated services digital network (ISDN) bearer channels often provide transport. In parallel with the PSTN, a packet based data network has evolved. This data network has largely been used for Internet traffic and data networking, and is mostly based in the internet protocol (IP). Although these networks have been mostly separate until recently, the two networks are starting to merge to create a so-called xe2x80x9cunified network.xe2x80x9d It is likely that future growth, at least in the developed countries, will be mostly accommodated by growth in IP based, packet networks.
As the PSTN evolved, it became desirable to provide many new, intelligent services such as caller-ID, automated callback, call forwarding, local number portability, and other custom calling features. To enable this new network intelligence, signaling information messages between switches in the telephone network are exchanged on a separate physical circuit or channel dedicated to that purpose. To support a separate signaling path running throughout the telephone network, an advanced intelligent network (AIN) was developed which operates in parallel with the voice circuit network of the circuit-switched telephone system. Today, the AIN uses a messaging protocol called signaling system 7 (SS7) to exchange call information between switches. SS7 is based on a set of international standards for highspeed digital communications and serves as the foundation for telephony infrastructures worldwide. In SS7, a layer of the protocol called the Transaction Capabilities Application Part (TCAP) handles queries and responses for databases. Other layers of the protocol include Message Transfer Part 2 (MTP2) and Message Transfer Part 3 (MTP3), and the Signaling Connection Part (SCCP). The SS7 standards are well known. For further information see Telcordia Technologies, GR-246-CORE, Specification of Signaling System Number 7, December, 1999, which is incorporated herein by reference. The capabilities of SS7 have been extended by another layer, called Intelligent Network Application Protocol (INAP). A network which features this protocol is called an Intelligent Network (IN). INAP is described in European Telecommunication Standards Institute (ETSI) Publication, ETSI-CORE-INAP-CS2, Intelligent Network Application Protocol, Capability Set 2, March, 1996, which is incorporated herein by reference.
Reliable, flexible, multimedia and voice traffic over IP networks has been enabled by the Session Initiation Protocol (SIP) as described in Internet Engineering Task Force (IETF) Request for Comments (RFC) 2543: Session Initiation Protocol, March 1999, which is incorporated herein by reference. SIP is an application layer control protocol that is used to establish, modify, and terminate multimedia sessions or calls. SIP provides proxiable messages used to perform call setup, modification, and termination functions. For example, one SIP message used to perform call setup functions is the INVITE message. The INVITE message is conventionally used to invite telephony devices to participate in a media stream communication, such as a voice communication, a data communication, a video communication, or any combination thereof. The INVITE message includes a session description protocol (SDP) portion that is used by end user devices to exchange media capabilities and other information.
As unified networks emerge, it is becoming increasingly important to provide calling services seamlessly across SIP based packet, networks and traditional AIN based signaling networks. In fact, this capability will become critical, as eventually, some new services will be provisioned only in the SIP based network. It will be desirable to access those services from the AIN based network, which will still be used for some time. The equipment and related protocols used to provide traditional AIN services are not readily adaptable to packet telephony networks. Currently, a few services have been provided across networks by using large, standing, centralized data-bases that slow down the routing of messages considerably. What is needed is a way to allow calling services to span cooperating circuit switched and packet switched networks, by seamlessly translating messages and responses between TCAP and SIP in a distributed manner, and in substantially real time.
The present invention solves the above problem by providing the capability to extend AIN services transparently between circuit switched and packet networks in a distributed fashion. Because the invention simplifies the provision of services that span the different network architectures, the services do not have to be fully deployed in multiple networks, and can therefore be deployed at lower cost. In one embodiment, the invention works by translating TCAP messages into SIP messages at each connection point between the two networks. SIP messages, which may be responses to the translated messages referred to above, are translated back into TCAP messages as appropriate. The proxy capability of SIP is used in conjunction with timers and default database entries to assure the circuit-switched network receives timely responses. It should be noted that any messages being handled will generically be referred to herein as xe2x80x9cmessages.xe2x80x9d However, the term xe2x80x9cresponsexe2x80x9d specifically refers herein to a message originating in one network in response to a message originating in another network.
According to an embodiment of the invention, a service control gate-way (SCG) is provided to translate messages being passed between the two networks. When the SCG receives a message from a first network, it stores network specific data from the message in an interaction database. The interaction database is a data structure maintained at the SCG to store information pertaining to a message as it traverses the unified network. The SCG determines network specific data for the second network that corresponds to the network specific data for the first network and stores that data in the interaction database. The message is then sent to a second network using the second network specific data so that the message is properly formatted. A response is received from the second network and is associated with the original message using information in the interaction database. The response is then formatted for the first network and sent to the first network for processing. In one embodiment, the first network is a circuit switched, AIN network using the SS7 protocol, and the second network is a packet network using SIP.
The interaction database, as referenced above, can be maintained within the memory system of the SCG. The database enables the fast translation of TCAP messages into SIP messages, and vice versa. The interaction database includes AIN network specific information, including a transaction identifier, session parameters, and routing data, corresponding to a message. The interaction database also includes SIP network specific information, including a call identifier and a sequence number corresponding to the message. All of the network specific information is accessible by a computer program that enables the service control gateway to translate messages and responses so that they can be passed between the two networks. In one embodiment, the information in the interaction database is organized into interaction data units (IDU""s). Information in the database is created as needed, maintained until the transaction is completed, and then erased. Multiple SCG""s can be used, one at each connection point between the networks, effectively distributing interaction databases across the IP network entry points. This distributed database structure, together with the capability to maintain only data needed for current transactions, makes the translation provided by the SCG""s much faster and more efficient than would be possible with a standing, centralized database.
The service control gateway is a hardware platform that includes connections for the two or more networks being spanned, and one or more processor units that control the operation of the SCG. The processors access a memory system, which includes the computer program code that implements the method of the invention, as well as the interaction database described above. The software and hardware in the SCG also provide a default response to the AIN if a message times out or a response cannot be sent from the packet network. The SCG is deployed between two constituent networks, a circuit switched network and the SIP based, packet switched network. The SIP network preferably includes a number server which can proxy INVITE messages for other entities within the SIP based constituent network.
As previously mentioned many aspects of the invention are implemented by computer program code. The computer program code together with the hardware described above provides the means to perform the functions of the universal mediation point. The computer program code can be stored independently from the device or transported over a network for shipping, back-up, or archival purposes. If the code is stored, storage media is used. The media can be magnetic such as diskette, tape, or fixed disk, or optical such as a CD-ROM.